A newer process developed by Monsanto for the purification or isolation of H2 from gas mixtures is based on separation through semipermeable membranes. The gas mixture flows around an array of hollow fibers, and only hydrogen and helium can diffuse into the fibers through their semipermeable polysulfone- coated walls. Separation from CH4, CO, O2, and N2 can be accomplished in this way. Monsanto has installed these H2 separation units (Prism separators) on an industrial scale worldwide for the regulation of the H2/CO ratio for 0x0 synthesis and for the recovery of H2 from flue gases in hydrogenation and NH3 plants.